Dear All, I appreciate the efforts and support of members/admin here toward the goodness of education. I am confusing a few concepts regarding diffraction, kindly help me out. I came up with following questions, 1. Is apperture required for diffraction or any finite wave will diffract? To me considering finite wave will have somewhere an apperture, it should diffract. 2. If apperture is smaller than wavelenght do we get diffraction? 3. By huygens principle the wave diffract and must enlarge, how do we get fourier transform (smaller in size usually for plane or spherical wave) in fresnel or franhofer plane. 4. Free space only add phase to propagation or also cause wave to diffract. (I think it do both) Kindly also recommend any good book on diffraction that covers diffraction due to free space and fourier imaging.